1. Field of the Invention
The present invention relates to a charger that charges a battery while detecting the temperature of the battery to be charged.
2. Description of the Related Art
Chargers that charge rechargeable batteries of AA battery, AAA battery and so on while detecting the battery temperature have been developed. Charging of batteries, if the battery temperature abnormally rises causes deterioration of battery performance. For this reason, chargers charge batteries while detecting the battery temperature. When a battery is charged, its temperature rises. Particularly, when a battery is close to full charge, its temperature sharply rises. An abnormal rise of battery temperature causes deterioration of battery characteristics. In order to prevent deterioration of battery performance, a charger that has a temperature sensor for detecting the battery temperature has been developed (see Japanese Patent Laid-Open Publication TOKUKAI No. 2002-199609 and Japanese Patent Laid-Open Publication TOKUKAI No. HEI 5-30669).
There are many types of chargers that detect the temperature of rechargeable batteries that are mounted to a battery mounting portion and in direct contact with a sensor. Typically, a temperature sensor such as a thermistor is disposed in a gap between cylindrical batteries that are arranged in parallel to each other, and thus, the battery temperature is detected. However, it is difficult for a charger of this type of structure to accurately detect the battery temperature. The reason is that temperature detection precision of temperature sensor depends on its environment. This causes variation of the detection temperature depending on the air temperature around the temperature sensor. In particular, in the structure that has a temperature sensor disposed on the side of a battery and a cooling fan disposed in a case for forcedly blowing cooling air on the rechargeable battery, the temperature sensor is cooled by the cooling air, and thus cannot accurately detect the battery temperature.
On the other hand, a charger having a temperature sensor such as a ceramic thermistor disposed not on the side of a battery but on the back side of a charging terminal of the charger for charging the battery has also been developed. In this structure, as shown in FIG. 16, a ceramic thermistor 94 is disposed on the back side of a charging terminal 97, and is thermally conductively connected to the charging terminal 97 with solder, or the like. However, this structure also cannot eliminate environmental influence of the temperature sensor. The reason is that, since the ceramic thermistor held on the back side of the terminal is exposed, it is affected by the environmental temperature of a battery.
In addition, a charger having a temperature sensor that is in contact with a terminal of a battery through the intermediary of a metal cylinder has also been developed. As shown in FIG. 17, this charger is provided with charging terminals 87 and a temperature sensor 84. The charging terminals 87 are made of elastically deformable metal plates by bending. The temperature sensor 84 is disposed close to the lower part of the contact portions 87a of the charging terminals 87, and detects the battery temperature. This temperature sensor 84 is pressed against a terminal of a battery through the intermediary of a metal cylinder 82. This metal cylinder 82 is made of an elastic metal plate 81 with top ends deformed in a cylindrical shape, and accommodates the cylindrical temperature sensor 84 in contact with each other. The elastic metal plate 81 elastically presses the metal cylinder 82 against a battery that is mounted in the charger. Since heat from the battery can be efficiently conducted to the temperature sensor 84 through the metal cylinder 82 that is pressed against the terminal of the battery, this structure has a feature that can quickly detect the battery temperature by the temperature sensor 84.
However, in this structure, it is necessary to insert the temperature sensor into the interior of the metal cylinder so that they are in contact with each other, and additionally to press this metal cylinder against the terminal of the battery through the intermediary of the elastic metal plate, and so on. For this reason, this structure has disadvantages that require time and effort for arrangement of the temperature sensor and the number of parts is increased, as a result, it is difficult to reduce manufacturing costs. In addition, in this structure, since the temperature sensor 84 and the metal cylinder 82 are disposed on the interior side of the charging terminals 87 (i.e., battery side), when a fan blows cooling air on the batteries to cool the batteries to be charged, the metal cylinder that is disposed on the battery side is often affected by the cooling air, or the like. Accordingly, there is a problem that the possibility of detection temperature error cannot be eliminated.